1. Field of the Invention
The present invention relates to a peaking capacitor layout used for a power-supply unit of a laser device.
2. Description of the Related Art
Recently, a lot of magnetic pulse compression circuits are used for the power-supply unit of a high power pulse laser device. The durability of main switches such as a thyratron and GTO is improved by using the magnetic pulse compression circuit. The magnetic pulse compression circuit of such a type is known described in Japanese Patent Application Laid-Open Publication No. 5-167158.
FIG. 10 shows a capacitance transit type magnetic pulse compression circuit used for the power -supply unit of a pulse laser device. As shown in FIG. 10, one of plates of peaking capacitor Cp1 is connected to discharge electrode 2 (cathode) through electric signal line 11a. The other plate of the peaking capacitor Cp1 is connected to another discharge electrode 3 (anode) through electric signal line 11b. In other words, the peaking capacitor Cp1 is electrically connected in parallel to the discharge electrodes 2, 3 through loop (current circuit) Lp1. The discharge electrodes 2, 3 are disposed in a laser medium.
FIG. 11 shows a layout of peaking capacitors Cp1. FIG. 11 is a diagram showing the discharge electrodes 2, 3 viewed from their sides.
As shown in FIG. 11, a plurality of peaking capacitors Cp1 having the same capacitance are disposed in a row along the longitudinal directions of the discharge electrodes 2, 3. The peaking capacitors Cp1 are connected to conductor 9. The conductor 9 is electrically connected to the discharge electrode 2. A discharge is caused in discharge area 4 between the discharge electrodes 2, 3.
Then, when an unshown main switch is turned on in FIG. 10, electric charges are supplied to and accumulated in charging capacitor Cn. When a time integral of a recharging voltage of the charging capacitor Cn reaches a limiting value which depends on a predetermined characteristic of magnetic switch Ln, the magnetic switch Ln is saturated, and the electric charges are transferred to and accumulated in the peaking capacitor Cp1. The recharging voltage of the peaking capacitor Cp1 increases as the transfer of electric charges progresses. Then, when the recharging voltage of the peaking capacitor Cp1 reaches a predetermined main discharge start voltage, a laser gas between the discharge electrodes 2, 3 is undergone an electric breakdown, and the main discharge is started. The laser medium is excited by the main discharge, and laser light is emitted in several nsec.
Then, the recharging voltage of the peaking capacitor Cp1 is quickly lowered by the main discharge, and the state before starting the charging is resumed after a lapse of a predetermined period of time.
Such a discharge operation as above is repeated by the switching operation of the main switch, and a pulse laser is oscillated at a predetermined repetition frequency (pulse oscillation frequency).
FIG. 5 shows the waveform of electric current i flowing through the loop Lp1 of the peaking capacitors Cp1 and the discharge electrodes 2, 3. The horizontal axis in FIG. 5 indicates time t. The electric charges are transferred from the peaking capacitors Cp1 to the discharge electrodes 2, 3 over time xcfx841, and the discharge is caused between the electrodes 2, 3. The area surrounded by the current waveform in FIG. 5 corresponds to a magnitude (laser light power) of discharge energy between the discharge electrodes 2, 3.
The discharge energy becomes larger as a rising inclination of the current waveform becomes large and the transition time xcfx841 becomes shorter. It is known that the rising inclination of the current waveform can be made larger and the transition time xcfx841 shorter by reducing the capacitance of each peaking capacitor Cp1 in FIG. 11.
To decrease the capacitance of each peaking capacitor Cp1 in FIG. 11, it is necessary to increase the number of peaking capacitors Cp1 in one row so to have the same discharge energy.
But, the peaking capacitors Cp1 must be disposed in two rows in order to arrange many of them because the discharge electrodes 2, 3 have a limited length in their longitudinal directions.
FIG. 12 shows an example that the peaking capacitors Cp1 are disposed in a first row close to the discharge electrode 2 and the peaking capacitors Cp2 are disposed in a second row distant from the discharge electrode 2. The respective peaking capacitors Cp1, Cp2 have the same capacitance in FIG. 12 which is smaller than that of the each peaking capacitor Cp1 of FIG. 11.
FIG. 6 shows the waveform of electric current i flowing through the loop Lp1 of the peaking capacitors Cp1 in the first row and the discharge electrodes 2, 3 and the waveform of electric current i flowing through loop Lp2 of the peaking capacitors Cp2 in the second row and the discharge electrodes 2, 3 of FIG. 12.
The loop Lp2 is longer than the loop Lp1 because the peaking capacitors Cp2 in the second row are distant from the discharge electrodes 2, 3 as compared with the peaking capacitors Cp1 in the first row.
Because the peaking capacitors Cp1 in the first row of FIG. 12 have the capacitance smaller than the peaking capacitors Cp1 of FIG. 11, the electric charges are transferred to the discharge electrodes 2, 3 with an arising inclination larger and transition time xcfx842 smaller than those of the current waveform of FIG. 5. But, the peaking capacitors Cp2 in the second row of FIG. 12 have the capacitance smaller than the peaking capacitors Cp1 of FIG. 11, but the rising inclination of the current waveform is small and transition time xcfx843 becomes larger than the transition time xcfx842 because the loop Lp2 is longer than the loop Lp1.
Therefore, there is a problem that the discharge energy is canceled in the time xcfx843xe2x88x92xcfx842 and the discharge energy is lowered.
Accordingly, it is a first object of the present invention to prevent the discharge energy from lowering even when the peaking capacitors are disposed in a plurality of rows with their capacitance lowered and their quantity increased.
Where the peaking capacitors are disposed in two rows as shown in FIG. 12, the disposed intervals and quantity of the peaking capacitors become different between the first and second rows. The disposed intervals of the peaking capacitors Cp2 in the second row of FIG. 12 are larger than those of the peaking capacitors Cp1 in the first row, and the quantity of the peaking capacitors Cp2 in the second row is smaller than that of the peaking capacitors Cp1 in the first row.
Therefore, the peaking capacitors Cp1, Cp2 have nonuniform capacitance at the respective points in the longitudinal directions of the discharge electrodes 2, 3. The nonuniform capacitance of the peaking capacitors Cp1, Cp2 results in nonuniform dispersion of the discharge energy.
FIG. 9 is a conceptual diagram showing dispersion of discharge A when it was caused by the layout shown in FIG. 12.
As shown in FIG. 9, because the peaking capacitors Cp1, Cp2 have nonuniform capacitance at the respective points in the longitudinal directions of the discharge electrodes 2, 3, the discharge A also has a nonuniform dispersion as indicated by slanted lines. The nonuniform discharge means that stable laser power cannot be obtained.
Accordingly, it is a second object of the present invention to make the discharge energy dispersion uniform so to obtain stable laser power even when the peaking capacitors are lowered their capacitance, increased their quantity and disposed in a plurality of rows.
It is a first object of the first aspect of the invention to prevent discharge energy from lowering even when the peaking capacitors are decreased their capacitance, increased their quantity and disposed in a plurality of rows.
The first aspect of the invention is a peaking capacitor layout in a laser device, which includes discharge electrodes disposed in a laser medium and a single-row peaking capacitor group having a plurality of peaking capacitors which are electrically connected in parallel to the discharge electrodes through a current circuit and also disposed in a row along a longitudinal direction of the discharge electrodes, in which a discharge is caused across the discharge electrodes by transferring electric charges from the respective peaking capacitors forming the single-row peaking capacitor group to the discharge electrodes in a predetermined transition time to excite the laser medium, wherein:
the single-row peaking capacitor group is disposed in plural numbers in a direction in which a length of the current circuit varies, and
a capacitance of each of the peaking capacitors forming a row with a longer current circuit is adjusted to be smaller than that of the peaking capacitors forming a row with a shorter current circuit so to reduce a transition time difference of the peaking capacitors in the respective rows.
According to the first aspect of the invention, the peaking capacitor group in the first row consisting of the plurality of peaking capacitors Cp1 and the peaking capacitor group in the second row consisting of the plurality of peaking capacitors Cp2 are disposed in a plurality of rows (two rows) in the directions that the loop Lp1 (indicated by a broken line) and the loop Lp2 (indicated by an alternate long and short dash line) have a different length as shown in FIG. 1.
The capacitance of the peaking capacitors Cp2 forming the second row with the long loop Lp2 is adjusted to be smaller than that of the peaking capacitors Cp1 forming the first row with the short loop Lp1.
FIG. 7 shows a waveform of current i flowing through the loop Lp1 of the peaking capacitors Cp1 in the first row and the discharge electrodes 2, 3 and a waveform of current i flowing through the loop Lp2 of the peaking capacitors Cp2 in the second row and the discharge electrodes 2, 3 of FIG. 1. The loop Lp2 is longer than the loop Lp1 because the peaking capacitors Cp2 in the second row are distant from the discharge electrodes 2, 3 as compared with the peaking capacitors Cp1 in the first row.
The peaking capacitors Cp1 in the first row of FIG. 1 have capacitance smaller than the peaking capacitors Cp1 of FIG. 11, so that the electric charges are transferred to the discharge electrodes 2, 3 at a larger rising inclination in shorter transition time xcfx842 than the current waveform of FIG. 5. Here, the peaking capacitors Cp2 in the second row of FIG. 1 are adjusted to have capacitance smaller than the peaking capacitors Cp1 in the first row of FIG. 1. Because the peaking capacitors Cp2 in the second row have small capacitance, the peaking capacitors Cp2 in the second row have the same transition time as the transition time xcfx842 of the peaking capacitors Cp1 in the first row though the loop Lp2 is longer than the loop Lp1. Therefore, the cancellation of the discharge energy as shown in FIG. 6 does not take place, and the discharge energy can be prevented from lowering.
It is a second object of a second aspect of the invention to make a discharge energy dispersion uniform so to enable to obtain stable laser power even when the peaking capacitors are decreased their capacitance, increased their quantity and disposed in a plurality of rows.
The second aspect of the invention is directed to the first aspect of the invention, wherein the capacitance of the peaking capacitors forming the peaking capacitor groups of the two or more rows is adjusted so to make a capacitance dispersion of the peaking capacitors uniform along the longitudinal direction of the discharge electrodes.
According to the second aspect of the invention, the capacitance of the peaking capacitors Cp1, Cp2 in the first and second rows is adjusted so to be uniformly dispersed along the longitudinal directions of the discharge electrodes 2, 3 as shown in FIG. 3. Specifically, the peaking capacitors Cp2 in the second row are disposed at the same intervals as those of the peaking capacitors Cp1 in the first row, and the quantity of the peaking capacitors Cp2 in the second row is adjusted to be the same as the peaking capacitors Cp1 in the first row.
Therefore, the peaking capacitors Cp1, Cp2 have the same capacitance at the respective points along the longitudinal directions of the discharge electrodes 2, 3. The discharge energy dispersion becomes uniform because the peaking capacitors Cp1, Cp2 have the uniform dispersion of capacitance. Thus, stable laser power can be obtained.